Kirchhoff’s Current Law Under Parallel Temperature Gradient: The Fundamental Principle Governing Thermoelectric Generator

We unveil a long-unrecognized fundamental principle that governs thermoelectric generator performance. Thermoelectric generator is traditionally treated as voltage-producing device whose output current is determined by the external load. Here, we demonstrate that under a parallel temperature-gradient field, Kirchhoff’s Current Law imposes a decisive constraint: the operating current is dictated exclusively by the ‘weaker’ leg, which refers to the P- or N-type thermoelement with the smaller intrinsic short-circuit current. This physical insight leads directly to a universal design rule based on their individual short-circuit currents: I_"sc" ^P=I_"sc" ^N. By applying this principle to PbTe-based module, we achieved a conversion efficiency of 15.2%, significantly surpassing the previous record, which had remained below 11%. This discovery reframes the intrinsic operating mechanism of thermoelectric generator and establishes a practical design methodology for achieving breakthrough performance.